Cohesive zone modelling of hydrogen assisted fatigue crack growth: the role of trapping

TL;DR

This paper presents a new modeling approach to understand how microstructural traps influence hydrogen-assisted fatigue crack growth, highlighting the roles of loading frequency and trap density in embrittlement.

Contribution

It introduces a novel formulation combining multi-trap diffusion, strain gradient plasticity, and a hydrogen-dependent cohesive zone model for fatigue crack growth analysis.

Findings

Higher beneficial trap density reduces crack growth rates.

The ratio of loading frequency to diffusivity controls crack growth behavior.

Optimal trap densities and frequencies can minimize embrittlement.

Abstract

We investigate the influence of microstructural traps in hydrogen-assisted fatigue crack growth. To this end, a new formulation combining multi-trap stress-assisted diffusion, mechanism-based strain gradient plasticity and a hydrogen- and fatigue-dependent cohesive zone model is presented and numerically implemented. The results show that the ratio of loading frequency to effective diffusivity governs fatigue crack growth behaviour. Increasing the density of \emph{beneficial} traps, not involved in the fracture process, results in lower fatigue crack growth rates. The combinations of loading frequency and carbide trap densities that minimise embrittlement susceptibility are identified, providing the foundation for a rational design of hydrogen-resistant alloys.